Engine timing and balancing mechanism



N0V- 5, 1963 R. R. BEKKALA ETAL 3,109,417

ENGINE TIMING AND BALANCING NECHANISN Filed Jan. 9, 1962 Y 2 Sheets-Sheet l IN V EN TOR. 247/1 @g/m@ ...Kip iilt,..., EN

NOV 5, 1963 R. R. BEKKALA ETAL 3,109,417

ENGINE TIMING AND BALANCING MECHANISM Filed Jan. 9, 1962 2 sheets-shea 2 INV EN TOR.

ATTORNEY `the invention is not 3,109,417 ENGINE TlMlNG AND BALANCING MECHANISM Ralph R. Beklrala, Detroit, and Harvey G. Humphries, Birmingham, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Jan. 9, 1962, Ser. No. 165,182

Claims. (Cl. 12S- 90) This invention relates lgenerally to an internal combustion engine land particularly contemplates a servo mechanism operable to modify the operative cyclic timing and thus the power output or energy absorbing characteristics of an internal combustion engine without disturbing the phased relationship of associated eng-ine balancing means.

The instant application and the invention herein described represents a continuation-in-part improvement of the servo mechanism shown and described in co-pending United States patent application Serial No. 94,887, entitled Phase Adjusting Servo Mechanism yfor Internal Combustion Engine and the Like, filed March 10,` 1961, in the names of Ralph R. Bekkala and Harvey G. Humphries. The servo mechanism of the invention thus has particular application .for varying camshaft timing of exhaust valve opening in a two-cycle uniflow scavenged internal combustion engine of the type shown and described in United States Patent No. 2,179,709, to A. F. Brecht, entitled Internal `Combustion Engine. Such camshaft timing adjustment permits conversion of the engine from its normal engine power generati-ng cycle to that of an energy absorbing compressor capable of providing variable braking action of an associated engine driven load such as a motor vehicle. With the phase adjusting servo mechanism of the above-identified patent application, the driven phased relationships between the several balancing weights or masses are necessarily compromised, at least during periods of compressive engine braking. The instant servo mechanism eliminates such compromising of the auxiliary engine balancing means.

Although having particular application for compressive engine braking purposes, the servo mechanism of deemed to be so limited, being applicable generally to angular phase adjusting mechanisms operable to selectively adjust the phase relation between a driven power input member and certain driven load members while maintaining the phased relationship `between the input member and ycertain other driven load members such as the instant phased balancing masses.

The-foregoing and other objects, advantages and features of the invention will be apparent from the following description of an illustrative embodiment, having reference to the accompanying dra-wing, in which:

FIGURE l is a fragmentary View of Ia portion of an internal combustion engine incorporating the invention with por-tions thereof broken away and shown in section substantially in the direction o-f the arrows and in the pla-ne of the line indicated at 1--1 of FIGURE 3;

FIGURE 2 is a perspective view of la servo controlling valve member shown in section in `FIGURE 1; i y

FIGURE 3 is a fragmentary elevational view taken substantially in the direction of the arrows indicated at 3--3 of yFIGURE 1 with portions thereof broken away and shown in section;

FIGURE 4 is a view similar to a portion of FIGURE 3 with other portions thereof broken away and shown in section substantially in the direction of the arrows and in the plane of the line indicated at 4-4 of FIGURE 1; and

`FIGURE 5 is a diagrammatic view showing application of the servo mechanism of the invention to the bal- United States Patent() 3*,i9,417 Patented Nov. 5, 1963 ice ancing system to a two-cycle internal gine of the type indicated.

Referring more particularly to FIGURE 1, an engine frame member is partially shown at 10` and has a camshaft mounting gallery 12 extending longitudinally therethrough. A gear housing member partially shown at 14 is suitably and sealingly secured to the end wall of the frame member and has an opening 16 mating with the camshaft gallery. A hollow camshaft 18 is rotatably supported within the camshaft gallery by a plurality of longitudinally spaced bearings, only one end bearing being shown at 20. This end bearing `comprises a cylindrical bearing support -member 22 having a sleeve portion slidably embraced by the aligned housing and frame defined gallery openings and having a radial end flange 24 suitably secured to the gear housing adjacent the opening 16. Two bearing sleeves 26 are axially spaced within theV sleeve portion of the support member and rotatably support the adjacent camshaft end journal portion 28. thrust bearin-g washer 30 is interposed between the cylindrical end of the bearing support member Z2 and a thrust shoulder 32 formed integrally of the camshaft.

The annular groove 3-4 defined between the spaced bearing sleeves 26 communicates through a radial port `i6 and a circumferential outer groove 33 in the bearing sleeve portion with a pressurized oil supply passage 40 in the engine frame member. The camshaft is longitudinally drilled at 42 to define an oil distribution gallery. This gallery .is connected through radial ports to its several journal portions and bearings. The camshaft is counterbored at y44 from its gear housing projecting end through its adjacent end journal portion. The counterbore 44 is connected through radial ports 46 in the camshaft journal portion 28 to the annular oil pressure supply groove 34 of .the bearing 20. The counterbore 4-4 is also connected to the camshaft oil distribution gallery 42 through a liow restriction 48 :defined between a sleeve `50 seated `at one end against the shoulder of the counterbore and a shaft 52 closely embraced by and extending through the oil gallery defining bore and counterb combustion enore.

A hollow valve member 54 is reciprocably mounted in the opened end of the camshaft counterbore 44 and slid-ably embraces the adjacent end of the shaft 52. As best seen in FIGURE 2, this valve member comprises a cylindrical valve portion 56 iand a relatively iiat guide or key portion 76 extending axially therefrom. The cylindrical valve portion has sliding sealing engagement outwardly with the camshaft counterbore and inwardly with a seal land 58 formed circumferentially of the inner shaft 52. The valve portion thus defines a cylindrical oil receiving chamber 60 between the shaft 52, the counterbore 44 and the sleeve 5t).` The valve portion 56 is helically relieved yfrom opposite ends at 62.` and 64 to form a pressure inlet port and a pressure relieving outlet port, respectively. The :inlet port is connected at 66 to the chamber 60 and therethrough to the oil pressure supply. The helical pressure relieving outlet port is connected at '68 to the interior of the gear housing member and therethrought the oil sump of the engine, not shown. Reciprocation of the valve member and the effected rotation of the camshaft relative thereto cause the valve member to alternately control the supply and discharge o-f oil pressure to and from the servo motor through two radial ports 72 and 74 spaced longitudinally of the camshaft journal position.

The relatively iiat guide portionrof the valve member intersected by an extension of the shaft embracing bore of the valve portion and thus defines two legs 78 and flanking the end portion of the shaft 52 on opposite sides thereof. The legs 78 and 80* are interconnected at 3 d their ends ldistal 'from the valve portion 56 by a bight haust valve opening. As previously indicated, such oil 82 and an actuating head 84 formed integrally therewith. pressure supply and the resultant camshaft timing adjust- The head V84 is thrustably engageable by a member acment is regulated by longitudinal positioning of the valve tuated by a suitable engine phase, load or power conmember 54. The valve member is non-rotatably maintrolling device, such as a vehicleV brake energizing pedal, 5 tained with respect to the gear member 104 by a coi an engine throttle control, ior an engine or vehicle -speed bined valve guide and balance weight member 138. This limiting governor. The servo controlling valve is inovweight member is suitably secured with a second arcuate .able by such .a control device beween an extreme cambalance weight member 140* to the wall portion 112 of shaft retarding position, shown in FIGURES 1 and 3 the gear member. The weight and guide member 138 has and corresponding to normal engine cycle operation, and l0 a hub portion 142 internally splined at A1414 to the adjaan extreme camshaft advancing position wherein corncen-t end of the shaft 52 and slotted at 146 to reciprocably -pressive cycle operation is effected by the engine. A valve receive the guide legs I8v and 80 of the valve member 54. return spring 86 embraces the sha-ft 52 and is compres- The shaft 52 and valve member 54 are thus drivingly conslvely interposed between the Opposing ends 0f the sleeve neCted fOr rOtalOu With the Combined gear and balance 50 and the cylindrical valve portion 56 within the pres- 15 Weight assembly- 'sure supply chamber 60. This spring normally acts in The opposite end ofthe Shaft 52 Projects Slightly beyond conjunction lwith the supplied oil pressure to bias the the end of the camshaft distal from the servo motor gear valve member toward its eXtreme camshaft retarding posi- 90- The adjacent end of the Camshaft Oil gallery 42 is tion, sealed by a seal ring 148. The camshaft has a reduced In addition to the control valve mechanism defined by ldinneter J'Ournal bearing portion 150 which extends bethe valve member and the porting of the adjacent caniyong its end Journal Portion 152 This reduced dlameter shaft end portion, the illustrative engine cycle or phase hearing Portion Journals an aUXlllary englne halanelng adjusting mechanism includes a combined camshaft driv- Weight member 154 which 1s secured on the camshaft end reference numeral 90.A This combined gear and motor n thrust hearing Washer 158 by a not 150- The halanee which carries three equiangularly spaced, radially extend- The Center of Innss ofthe gear driven balance Weights 133 dowel pins, as shown balance weights cooperate with the similarly disposed drical flange I114. The opposite end of this harige is seal- A gear member 10'4 is rotatably mounted with respect to 35 haldhoe masses of the gear and Weight mounted on OP nut .110i threaded on the adjacent cnd of the camshaft. A ancing weights irrespective of timing adjustment of the wall portion 1-12 of fthe gear member extends radially outt camshaft by ille driving Connection Provided by the wardly of thejournal opening l108 to one end of a cylinshaft 52- i Under no ingly joumeled at 115 ou the Outer periphery ofthe mem member 54 is maintained in its spring and oil pressure ber .92 'to define .the annular Chamber 10u therebetween 45 biased camshaft retarding position vshown in FIGURE l. inwardly, the wall 1'12 has rotative sealing clearances with *in this Position, the helical Valve Port 62 serves to snPPly the spider and hub portions of thecamshaft driving mempressurized oil 'through the radial Port 72: the annular Vben plurality (if-gear tenth 11,6 arc formed circurn groove'13f4 and the passages 132 to the camshaft retarded FIGURE 5J .the gear teeth 1.16 nrt-nh with themating teeth 50 plied acts in conjunction with the torque loading imposed of a balance Weight gear 113 mounted On the adlnccnt on the camshaft by the several exhaust valve and fuel end of a balance shaft 119 The gear 118 rs ln turn driven injection actuating mechanisms to maintain the several through an idiergear nohvatirning gear 12.1 mounted on gear carried vanes 124 in driving engagement with the rand driven by the engine .crankshaft 1.22 A 'balance vanes 102 carried by the camshaft driving member, the W'elght 123 is Secured `to the oppositevend of the` shaft 119 55 several camshaft advancing expansible chambers 118 being with 'its mass diametrically and eccentrically disposed to Vented to ills gear, housing and sump ihrougiiihe Passages that of the `huittncc Shaft driving .gear 118 v 130, the groove 136 and the helical valve port 64. The Three vancs or ,piston members ,124 are equiangularly driving engagement effected between the servo niotor spaced and suitablysecured tortheradial wall portion 1-12 Varies Provides normal 'iifooyolo engine timing of the o f lthe gear member by radially spaced bolts and dowel 60 several eXhaUStVaiVes pms, Ves Shown 'These vanes cooperate with the vancs In two-cycle internal combustion engines of the type 102120 subdvidethe annular.chamberY into `plurality Y indicated, fuel supply is normally accomplished by presseveral expansible motor chambers 126 and 128 are coninlectilig means 1S normally regulated between no fuel neeted respectively through passages 13,0 and 132 in the 65 and full fuel supply conditions through the operation of a camshaft driving member 92 to two annular charnhc'rs throttle control between governor maintained minimum or 'grooves 134 and 136 opening inwardly and spaced and maximum engine speed limits- When the throttle mate respectively with `the vnlve cOntrolled radial ports vehicle is moving and driving the engine at a'speed in ex- 72 and 74 in the camshaft cnd portion 70 cess of engine idle speed, the speed responsive mechanism ith counterclockwise driving rotation of the camshaft of e governor aetuates the fuel sUPPly regulating means as. indicated 1n FIGURE fluid pressure alternately Supto its fuel olf position Under such conditions the driven plied to the expansibie chamber v126 and 12s effects relaengine absorbs a certain amount f enersyrand thus tends tive rotation between the camshaft driving and gear memto brake the vehicle. This braking effect is normally 5 dependent upon frictional load of the motored engine and of the various associated accessory loads, including the engine scavenging and charging blower and to a limited extent upon rthe energy required to compress the air charged within the several cylinders. The energyabsorbed in compressing the air charge within the several cylinders of a motored engine is normally limited to the period between exhaust valve closing at approximately 80 of crankshaft rotation past its bottom center up to its top center position. A substantial portion of this absorbed compressive energy, however, is normally returned to the engine crankshaft during the initial portion of the subsequent power stroke prior tto the opening of the exhaust valve which occurs between 85 and 100 of crankshaft rotation past its top center position for each cylinder.

As indicated above, the servo control mechanism 90 is operable to advance the camshaft timing and thus the opening and closing of the several exhaust valves in accordance with the effected positioning of the valve member 54 relative to the radial valve porting of the camshaft. Such advancing of exhaust valve timing increases the compression period and the air charged volume subjected to compression and reduces or prevents compressive power return to the engine crankshaft. The engine is thus caused to operate as a variable capaci-ty compressor braking the inertial load of the engine and associated vehicle.

Limited longitudinal movement of the valve member 54 to the left as viewed in FIGURE 1 effects communication between the helical pressure supply port 62 and the camshaft radial port 74. Actuating oil pressure is thus supplied to the camshaft advance expansible chambers 128. At the same time, the helical pressure relieving valve port 64 opens the camshaft port 72 and thus starts to relieve the oil pressure previously supplied to the several radial expansible chambers 126. This causes camshaft advancing rotation between the camshaft driving and gear members 92 and 1h41 until the ports 72 and 74 are covered by the helical land extending between the valve ports 62 and 64. In this port closed position, limited leakage occurs between the several chamber defining members thus permitting pressure to build up on both sides of the several vane or piston members until a balanced iiuid pressure is obtained. This balanced pressure condition hydraulically maintains the camshaft in an adjusted position corresponding to the desired compressive braking effect indicated by the initial positioning of the valve member.

Should additional braking be desired, the valve member may be further shifted to the left wtih resultant further advancing of the camshaft until the ports 72 and 74 are again closed by the valve member and a new equilibrium pressure condition is achieved between the retard and advanced chambers. To reduce the braking effect, the valve member is permitted to return toward its camshaft retarding iiuid pressure supply position wherein the end of the cylindrical valve portion abuts the valve driving hub 142. Such valve movement to an intermediate valve position vents the several advancing chambers and supplies actuating oil pressure to the retarding chambers until a new equilibrium pressure condition is obtained as the ports 72 and 74 are again closed by the effected camshaft retarded rotation. Such valve movement thus retards the exhaust valve closing and opening and reduces the power absorbing compressive braking action of the engine.

1t will thus be seen that the servo mechanism 90 per- Vmits adjustment of the camshaft timing, converting the 4engine from its normal cycle to a compressive braking or load, without comprising the phased relationship of the several engine balancing weights associated therewith.

While the foregoing description has been limited to a single illustrative embodiment of the invention having particular application to an engine braking control, it will be obvious to those skilled in the art that various modifications might be made therein and other applications made without departing from the spirit and scope of the invention as dened in the following claims.

We claim:

l. In an internal combustion enginemeans for regulating the power output and compression timing characteristie of the engine including,

a hollow camshaft journaled Within and projecting at opposite ends from said engine,

an engine-driven servo mechanism mounted on one end of said camshaft and selectively operable to vary the angular phased timing relation between the camshaft and engine output thereby varying the power output and compression timing characteristics of the engine,

a first engine balancing mass carried and rotatably driven by said servo mechanism eccentrically of the camshaft in timed phased relation to the engine output:

a second engine balancing mass journaled on the opposite end of said camshaft,

and shaft means extending through said camshaft and drivingly interconnecting said second engine balancing mass for rotation with said first balancing mass in timed phased relation to the engine output irrespective of the camshaft timing adjustment effected by said servo mechanism.

2. ln an internal combustion engine, an engine timing and balancing system including,

an engine-driven crankshaft,

a hollow camshaft journaled within the engine and rotatably operable to sequentially operate associated exhaust valves,

a servo mechanism mounted on one end of said camshaft,

gear means drivingly interconnecting said servo mechanism to the crankshaft of the engine and said servo mechanism being selectively operable to vary the angular phased timing relation between the camshaft and engine crankshaft and thereby the power output and compression timing characteristics of the engine,

a first engine balancing mass carried by said servo mechanism eccentrically of the camshaft and driven in timed phased relation to Ithe engine crankshaft,

a second engine balancing mass journaled on the opposite end of said camshaft,

and shaft means extending through said camshaft and rotatably driving said second balancing mass with said first balancing mass in timed phased relation to the engine crankshaft irrespective of .the camshaft timing adjustment effected by said servo mechanism.

3. In a two-cycle internal combustion engine, an engine, an engine balancing and timing mechanism operable to modulate the cyclic timing of the engine thereby regulating its power output and compression timing characteristics, said mechanism comprising,

a hollow camshaft journaled in and projecting at opposite ends from said engine and rotatably operable to time the scavenged exhausting and charging of the several engine combustion chambers,

passage means for supplying pressurized oil to the bore of said camshaft,

a rst member drivingly secured to one end of said camshaft, a

a second member rotatably and sealingly mounted with respect to said first mmeber and cooperating therewith to define an annular chamber,

means for driving said second member in angular relation to the engine output,

said first and second members each having equiangularly spaced radial varies cooperating to divide said annular chamber into a first and second plurality of paired opposing expansible motorchambers,

passage means connecting the opposing pairs of said expansible chambers to longitudinally spaced and timed phased a,1os,417

end of the engine irrespective of the servo adjusted angular positioning of the camshaft.

5. In a two-cycle internal combustion engine, an engine balancing and timing mechanism operable to counterbalance rocking couples acting on opposite ends of the engine and to regulate the cyclic timing and thereby the power output and compression timing characteristics of angularly disposed ports opening inwardly of said camshaft bore,

a hollow valve member reciprocably and rotatably mounted Within said camshaft bore,

centrically of the rotative axis of the camshaft, said valve means being operable to connect said first Yphased relation to the engine output and cooperating with said third balancing member to counteract the rocking couple normally applied to the adjacent the engine, said mechanism comprising,

two spaced parallel shafts journaled in and projecting and second opposing chambers alternatively to said 10 at opposite ends from the engine, at least one of said pressure supply means and to vent fluid pressure shafts beingl a hollow camshaft operable to sequentherefrom dependent on the axial positioning of said tially control the scavenged exhausting and charging valve member and the adjusted angular position of of the several engine combustion chambers,

said first and second members, means for supplying pressurized oil to the bore of Va second engine balancing member journaled on the said camshaft,

opposite end of said camshaft and having a balanca hub member drivingly secured to one end of said ing mass disposed eccentrically of the camshaft rocamshaft,

Y tative axis, a rst gear and engine balancing member rotatably Y and a shaft member extending longitudinally through and sealingly mounted with respect to said hub said camshaft and valve member and drivingly conmember and cooperating therewith to define an annecting said l second balance weight member to nular chamber and having an engine balancing mass said first weight member diametrically opposite the disposed eccentrically of the rotative axis of the cambalancing mass of said first weight member thereby shaft, driving said second balance weight in timed phased said hub and first gear members each having equiangurelation to said first balance weight and engine outlarly spaced radial vanes cooperating, to divide said put irrespective of the servol adjusted angular posiannular chamber into a first and second plurality of tioning of the camshaft. paired opposing expansible motor chambers operable 4. In an internal combustion engine, an engine balto adjust the angular phased relation between said ancing and timing mechanism operable to counterbalhub and first gear member,

ance rocking couples acting on the engine and to regulate passage means connecting the opposing pairs of said the Compression timing and absorbing characteristics of expansible chambers to longitudinally and angularly ,the engine, said mechanism comprising, disposed ports opening on said camshaft bore,

two shafts journaled in parallel spaced relation, at least a hollow valve member reciprocable within said camone of said shafts being a hollow camshaft rotatably shaft bore and drivingly connected for rotation with operable to sequentially exhaust the several engine said first gear member `and alternately operable to combustion chambers, connect the paired opposing chambers through said a first gear and engine balancing member rotatably camshaft bore to said pressure supply means and to mounted with respect toV one end of said camshaft vent fluid pressure therefrom dependent on the axial and having its engine balancing mass disposed eccenpositioning of said valve member and the adjusted trically of the. rotative axis of the camshaft, angular position of said first and second members,

a second gear and engine balancing member secured a second gear and engine balancing member drivingly k0n the adjacent one end of the other of said shafts engaging said first gear member and secured on the and drivingly engaging said first gear member to adjacent end of the other of said shafts to effect couneffect counterrotation therebetween and having an Iterrotation between said shafts, eccentric balancing mass oriented to cooperate with gear means for driving one of said first and second gears fthe eccentric mass of said first member to counterin time phased angular relation to the engine output, balance the rocking couple normally acting on the said second gear member having its balancing mass adjacent end of the engine, disposed eccentrically of its rotative axis and oriented gear means driving one of said first and second gear in assembly to cooperate with the eccentric mass of and engine balancing members in time phased ansaid first gear and balancing member to counteract gular relation to the engine output, the normal rocking couple applied to the adjacent a `third engine balancing member secured on the opend of the engine,

` posite end of said other shaft and having an eccena third engine balancing member secured on the optric balancing mass diametrically opposite that of posite end of said other shaft and having its balancsaid second gear and balancing member, ing mass eccentrically and diametrically opposite a fourth engine balancing member journaled on the the balancing mass of said vsecond gear and balancend of said camshaft opposite said first gear and ing member, balancing member, t n a fourth engine balancing member journaled on the opa fluid pressure servo motor operable to adjust the anguposite end of said camshaft and having its balancing lar phased exhaust timing relation between said cammass oriented eccentrically and diametrically op-V shaft and first gear member in accordance with the posite the balancing mass of said first balancing controlled supply of fluid pressure to and from said member,

, motor, Y j Y and a shaft member extending longitudinally through and a shaft member extending longitudinally through Said Camshaft 39d Valve member and drivingly@- said camshaft and drivingly interconnecting and oriterconnectmg sa1d first and' fourth engine balancing enting the eccentric Vbalancing mass of said fourth members. thereby dnl/mg Sfld fourth balanfing mem' engine balancing member diametrically opposite the bier m medphasajd relftlonjto the egme Output balancing mass of said first balancing member therelonolclltgfltl lolfgnlnglcllpgb by dnvmg Sald furth balancmg member m timed the adjacent end of the engine irrespective of the servo adjusted angular positioning of the camshaft.

No references cited.

eee-lef- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 109 ,417 November 5, 1963 Ralph R. Bekkala et al.

or appears in the above numbered pat- It is hereby certified that err tters Patent Should read as ent requiring correction and that the said Le corrected below Column 6, lines 52 and 53, strike out "an engne,". line 66, for "mmeber'l read member Signed and sealed this 7th day of July 1964.

(SEAL) Attest:

EDWARD J BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents 

1. IN AN INTERNAL COMBUSTION ENGINE MEANS FOR REGULATING THE POWER OUTPUT AND COMPRESSION TIMING CHARACTERISTIC OF THE ENGINE INCLUDING, A HOLLOW CAMSHAFT JOURNALED WITHIN AND PROJECTING AT OPPOSITE ENDS FROM SAID ENGINE, AN ENGINE-DRIVEN SERVO MECHANISM MOUNTED ON ONE END OF SAID CAMSHAFT AND SELECTIVELY OPERABLE TO VARY THE ANGULAR PHASED TIMING RELATION BETWEEN THE CAMSHAFT AND ENGINE OUTPUT THEREBY VARYING THE POWER OUTPUT AND COMPRESSION TIMING CHARACTERISTICS OF THE ENGINE, A FIRST ENGINE BALANCING MASS CARRIED AND ROTATABLY DRIVEN BY SAID SERVO MECHANISM ECCENTRICALLY OF THE CAMSHAFT IN TIMED PHASED RELATION TO THE ENGINE OUTPUT, A SECOND ENGINE BALANCING MASS JOURNALED ON THE OPPOSITE END OF SAID CAMSHAFT, AND SHAFT MEANS EXTENDING THROUGH SAID CAMSHAFT AND DRIVINGLY INTERCONNECTING SAID SECOND ENGINE BALANCING MASS FOR ROTATION WITH SAID FIRST BALANCING MASS IN TIMED PHASED RELATION TO THE ENGINE OUTPUT IRRESPECTIVE OF THE CAMSHAFT TIMING ADJUSTMENT EFFECTED BY SAID SERVO MECHANISM. 